1. Field of the Invention
The present invention relates to an electrical connector, and particularly to an electrical connector mounted to a circuit substrate by use of solder balls attached to contacts.
2. Description of Related Art
Electrical connectors are commonly mounted on a printed circuit board (PCB) in an electronic device for implementing different functions. In order to meet the miniature requirements, the overall side of the electronic device becomes smaller and smaller. Consequently, the PCB mounted within the device becomes small as well. However, while the dimension of the device decreases, the functions of the device increase. As such, there is a need to install more and more connectors within a limited area of the PCB. In order to mount more and more connectors on the PCB while without increasing the surface area. The dimension of the connector must be reduced. This means the pitch between terminals within the connector have to reduce as well. As such, a high-density connector is required.
The trend of miniaturization has also been meet by using surface mount techniques (SMT) for mounting the connectors on the PCB. The confluence of the use of SMT and the required fine pitch of the connectors has resulted in approaching the limits of SMT for high volume, low cost operations. Reducing the pitch of the terminals increases the risk of bringing adjacent solder pads or terminals during reflow of the solder paste.
The use of ball grid array (BGA) for mounting the connector on the PCB has been developed. In a BGA connector, spherical solder balls attached to the contacts are positioned on conductive pads of a PCB to which a layer of solder paste has been applied, typically by use of a screen or mask. The connector and the PCB are then heated to a temperature at which the solder paste and at least a portion or all of the solder ball melt and the solder ball is fused to the conductive pad on the PCB. The use of BGA in connecting the electrical connector to the PCB has many advantages. It is important for most situations that the board-engaging surfaces of the solder balls are coplanar to form a substantially flat mounting interface, so that in the final application the balls will reflow and solder evenly to the planar PCB. Coplanarity of the solder ball is influenced by the size of the solder ball and its positioning on the connector. The final size of the ball is dependent on the total volume of solder initially available in both the solder paste and the solder balls. How to apply solder balls to the connector contacts for meeting the requirement of coplanarity is really a challenge to the manufacturer.
Connectors having solder balls attached to contacts thereof are disclosed in U.S. Pat. Nos. 6,093,035, 6,024,584, 6,079,991, 6164983, 6,325,644 and 6,042,389 all issued to Lemke et al.
The connector disclosed in U.S. Pat. No. 6,093,035 comprises an insulative housing defining a passageway extending from a mating surface toward a mounting surface thereof. A well is formed in the mounting surface in alignment with and communication with the passageway. A pin-type terminal is received in the passageway with a terminal portion extending into the well where a solder ball is fused to the terminal portion. The well locates the position of the solder ball in the lateral X-Y directions prior to attachment of the solder ball onto the terminal. The terminal portion does not touch the solder ball and thereby influence its Z direction location. However, fusing of the solder ball onto the terminal portion is assured by having a relatively uniform and adequate amount of solder, from solder paste placed in the well. Any variation in the distance between the terminal and the solder ball is absorbed by the variable volume of the solder paste placed in the well. Therefore, the position of the solder ball in the Z direction is ensured with respect to the mounting surface of the housing and the distance of the solder ball from the terminal portion of the terminal.
The connector disclosed in U.S. Pat. No. 6,042,389 includes a connector body defining a passageway extending from a mating surface toward a mounting surface thereof. A well is formed in the mounting surface in alignment with and communication with the passageway. A pin-type terminal is xe2x80x9cbottomedxe2x80x9d in the passageway by inserting the terminal until bottom shoulders engage passage bottom surfaces, thereby locating the terminal in a vertical downward position. The terminal has a solder tab extending into the well. A solder ball is positioned in the well before it is attached to the solder tab of the terminal. In order to retain the terminal in the passage, the well receives a large amount of solder paste placed therein. After reflow to attach the solder ball onto the solder tab of the terminal, the solder ball and the solder paste disposed in the well form a mass that fills and conforms to the shape of the well. As a result, the solder mass engages the bottom of the well to thereby prevent movement of the terminal upward out of the passage.
However, there exists a problem in the above-mentioned patents that since a large amount of the solder paste is placed in the well, wicking of the solder from the well up the terminal is significantly serious when the connector is subjected to a reflow process to fuse the solder ball onto the terminal. Although the terminal is provided with a coating or/and thermal break structure on a medial portion thereof, the solder wicking is still a problem since there exists a gap between the terminal and the passageway.
Hence, an improved electrical connector is required to overcome the disadvantages of the related art.
Accordingly, it is an object of the present invention to provide an electrical connector having a releasable cover for conveniently and reliably attaching fusible elements to pin-type terminals thereof
It is another object of the present invention to provide an electrical connector having a releasable cover for suction by a vacuum pick up device, thereby facilitating placement of the connector onto a circuit substrate.
In order to achieve the objects set forth, an electrical connector having a releasable cover attached thereto is disclosed in accordance with the present invention. The connector comprises a connector body defining a passageway in a mounting surface with a contact received therein. The contact has a tail portion adapted to be electrically connected to a circuit substrate. The cover has a top plate disposed on the connector body for suction by a vacuum pick up device and a pair of legs downwardly extending into the passageway. The legs form an opening adjacent to the mounting surface with the tail portion of the contact terminating therein. A fusible element has a portion disposed in the opening and fused to the tail portion of the contact.
Other objects, advantages and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.